The micro-optical device such as a micro-lens which is a minute lens, a micro-lens array where plural micro-lenses are arranged, a micro-mirror which is a minute mirror, a micro-mirror array where plural micro-mirrors are arranged and the like have played an important roll since the micro-optical devices are born around 1970 to the present.
As for an image displaying device utilizing the micro-optical device, there is a liquid crystal projector enabling image projection by a spatial optical modulator where a micro-lens array is disposed on the light injection side. The micro-lens array is formed by assembling plural micro-lenses which are a kind of a minute optical element.
The spatial optical modulator is configured to include plural spatial optical modulating elements assembled, having an aperture or a reflection part. In the spatial optical modulator, a light injected to the aperture or the reflection part of the spatial optical modulating elements is modulated by being transmitted or reflected.
In the liquid crystal projector, it is desirable that a projection image can be clearly viewed even in a bright place. As for the configuration for this, the micro-lens array is configured to oppose a pixel array of the transmission liquid crystal optical modulator in order to improve a numerical aperture and an efficiency of optical utilization (For example, see Non Patent Document 1).
Moreover, there is a liquid crystal projector where a reflection spatial optical modulator is utilized in the same way as the above described projector. It is one of the characteristics of the reflection spatial optical modulator that the numerical aperture thereof can be increased greater than the numerical aperture of the transmission liquid crystal spatial optical modulator. Thus, the pixel size can be reduced. There is another merit such that the micro-lens is not necessary for improving the numerical aperture and the optical utilization ratio. Such a reflection liquid crystal spatial optical modulator is made using a semiconductor manufacturing process by forming, in order, an electrical circuit for driving, a pixel electrode, a liquid crystal layer and the like on s Si substrate (for example, see Non Patent Documents 2 and Patent Document 1).
These are also called LYCOS (Liquid Crystal on Si) since the liquid crystal is disposed on the Si substrate.
Furthermore, another configuration is also suggested such that the pixel array of the reflection spatial optical modulator is disposed to oppose the micro-lens array for realizing high-performance such as improving the efficiency of the optical utilization, the numerical aperture, and the like (for example, see Patent Document 2).
As for the projector, a contrast ratio can be given as a barometer of the projector.
The contrast ratio is expressed by a luminosity ratio (bright state/dark state) between an image displayed in the bright state and the image displayed in the dark state. The bright state and the dark state are switched by a switching function of the liquid crystal.
The higher the contrast ratio is, the higher the performance is. Accordingly, a projector utilizing a reflection spatial optical modulator with a high contrast ratio is desired in the market.
In the projector utilizing the transmission spatial optical modulator and the reflection spatial optical modulator including the micro-lens array, the contrast ratio may be decreased due to a change of a polarization state. However, in the transmission spatial optical modulator, the linearly polarized light passes through the micro-lens only once. Moreover, the polarization state undergoes a change also only once.
On the contrary, in the reflection spatial optical modulator where the micro-lens array is disposed, the linearly polarized light passes through the micro-lens twice, i.e., back and forth. In other words, the probability of the change of the polarization state occuring may be twice as much as in the transmission spatial optical modulator. According to this, from the view of the contrast ratio, the transmission spatial optical modulator is superior to the reflection spatial optical modulator.
As for the size (or height) of the contrast ratio, the polarization state of the light coming and going in the projector is associated with the size (or height) of the contrast ratio.
In the projector, non polarized light projected from a white light source such as an ultra-high pressure mercury lamp is separated into two linearly polarized lights, i.e., polarized lights P and S by a polarization changing optical system.
It is known that when the separated linearly polarized lights are projected onto a screen via a projection lens, coming and going in the optical system in the projector without vitiating the polarization state, the high contrast ratio can be expected (as for the change of the polarization state, see Non Patent Document 3).    [Patent Document 1] Japanese Patent Application Publication No. 2000-137246    [Patent Document 2] Japanese Patent Application Publication. No. 11-258585    [Non Patent Document 1] Kenjiro Hamanaka, O PLUS E, 2000-3, Vol. 2, Vol. 3, and pp. 313 through 318    [Non Patent Document 2] E. G. Colgan, M. Uda, IBM J. RES. DEVELOP. VOL. 42. NO.3/4, 1998, and pp. 339 through 345    [Non Patent Document 3] Kunio Tsuruta, Applied Optics II, Baifukan, and pp. 234 through 240
However, if the polarization state is vitiated, which influences the contrast ratio in the optical system (for example, a principal axis of the polarization, an elliptical polarization, and depolarization), the light is permeated through in the dark state resulting in a factor of vitiating the contrast ratio.
The polarized light P may be converted to the polarized light S in the optical system (On the contrary, the polarized light S may be converted to the polarized light P). This is an intentional change of the polarization state. Thus, this is discriminated from the above described undesirable change of the polarization state.
When the micro-lens array is positioned to oppose the pixel (electrode) array of the liquid crystal reflection spatial optical modulator, the principal axis of the linearly polarized light is rotated in the micro-lens array. Further, if a reflection preventing layer is provided, the change of the polarization state is caused such as the elliptical polarization.
The change becomes conspicuous when the incident angle is great. Further, in the optical system of the liquid crystal projector where the liquid crystal reflection spatial optical modulator is used, since a polarization beam splitter is provided ahead of the liquid crystal reflection spatial optical modulator, if the polarization state is changed, the light is not rigidly separated in response to the polarization (the polarized lights P and S). Thus, even in the dark state, the light reaches the screen. Accordingly, the contrast ratio may be reduced.
On the other hand, in addition to the contrast ratio, a high definition of the image can be given as the performance barometer of the liquid crystal projector. This is expressed by a pixel size and a number of pixels. The smaller the pixel size is and the more the number of the pixels is, it can be said that the higher the definition of the image is realized.
It is true that the reflection liquid crystal spatial optical modulator is superior to the transmission liquid crystal spatial optical modulator in reducing the pixel size, but the reduction of the pixel size is regulated by the semiconductor manufacturing process at the moment.
Accordingly, an object is given to realize a reduction of the pixel size without being regulated by the semiconductor manufacturing process.